Absorbent articles are typically used in contact with skin. Some absorbent articles such as disposable diapers, feminine pads, panty liners, incontinence pads and the like are held in contact with skin to absorb body liquids or exudates, while other absorbent materials such as paper towels, hand towels, and wipers may be held in the hands to absorb liquid on the skin or other surfaces. In virtually every case, it is desired that the absorbent article or material keep liquids off the skin to provide a clean, dry feel and to reduce skin health problems that arise from excess hydration or from contact with harmful biological or chemical materials in the liquid being absorbed.
While paper towels and wipers are often composed of a homogenous material, such as an entirely cellulosic web, absorbent articles intended to absorb body fluids typically have at least three layers of different materials. Next to the user's skin is a topsheet layer, sometimes herein referred to as a liner, body-side liner or cover sheet. Beneath the topsheet is the absorbent core that is designed to retain liquid, and beneath the absorbent core is a fluid-impervious backsheet that prevents leakage and maintains the integrity of the product. The topsheet should feel soft and should have high liquid permeability to allow body fluid such as urine, menses, or runny bowel movement to be absorbed and transported away from the skin to reach the central absorbent core. Ideally, the topsheet provides a “dry touch” or “dry feel” by preventing liquid from flowing back to the skin. It is also desirable that the topsheets have high wet resiliency to maintain their bulk and shape when wet.
Traditional hydrophilic cover materials or topsheets in contact with the skin can serve effectively to transport body fluids into the absorbent core, but they cause a wet feel against the skin of the user and may adversely affect skin health. Further, they may wick liquid in the plane of the layer, allowing liquid to approach the edges of the absorbent article and possibly leak or seep out.
To achieve the goal of softness and a dry feel in topsheets of absorbent articles, many manufacturers have turned to nonwoven fabrics made of hydrophobic fibers for the body-contacting topsheet. While the use of hydrophobic nonwoven fabrics may have resulted in improved dry feel, the hydrophobic material hinders wicking into the absorbent core, offers little absorbent capacity and reduces liquid permeability. Further, the poor absorbency of most hydrophobic materials causes any liquid retained therein to be easily squeezed out by body motion of the wearer.
Others have sought to improve the poor wicking and absorbent properties of hydrophobic materials by applying a finish comprising surfactants on the surface of the hydrophobic fibers. This approach may offer some benefits when the article is first wetted, but the surfactants tend to be washed away, resulting in poorer performance upon further wetting.
In the case of absorbent pads for feminine care, two distinct approaches involving hydrophobic topsheets or covers are common. One approach is to use a soft, clothlike nonwoven hydrophobic material, which increases comfort but has the drawback of poor intake of menses. Another approach is to use an apertured plastic film of hydrophobic polymer or other materials. The hydrophobic cover material repels many body fluids, while the apertures allow wicking away from the cover into the absorbent material beneath.
In theory, the hydrophobic apertured material should allow the user's skin to remain relatively dry while allowing wicking in the z-direction (normal to the plane of the cover) into the underlying absorbent core. In practice, hydrophobic apertured films present a number of problems. Apertured films have the drawback of being disliked by some users for their plastic feel and for their poor absorbency. Their hydrophobic nature resists transport through the material, possibly delaying wicking into the absorbent core. Likewise, pockets or pools of liquid may form between the film and the user's skin. In the absence of hydraulic pressure or physical compression, menses in particular may pool on the hydrophobic surface and not penetrate into the apertures, especially if there is a significant interfacial gap between the cover and the underlying absorbent material.
Therefore there is a need for an improved topsheet material which provides the clean feel said to be characteristic of hydrophobic topsheet materials, while also providing for rapid z-direction (depthwise) transport of liquid through the topsheet into the underlying absorbent core, a characteristic more typical of hydrophilic materials. Preferably, these absorbent topsheets also have wet resiliency and absorbency properties which persist upon multiple insults of urine or other liquids.